1. Field of the Invention
The present invention relates generally to workpiece transfer equipment in a dicing machine, and more particularly to workpiece transfer equipment in a dicing machine which efficiently transfers a workpiece to a workpiece cutting part, a workpiece cleansing part, etc.
2. Description of Related Art
Japanese Patent Provisional Publication No. 60-214911 has disclosed a dicing machine. This dicing machine has a reference position where a wafer which is supplied from the cartridge storing a number of wafers is pre-aligned, a second position where the wafer is loaded and unloaded on and from the cutting table, a third position where the cut wafer is cleansed, and a fourth position where the cleansed wafer is unloaded. The wafer which has been loaded on the cutting table at the second position moves with the cutting table and is finely aligned, and then the wafer is cut into desired semiconductor chips with a diamond cutter, etc. Then, the cut wafer is transferred to the third position, where the wafer is cleansed.
The above-mentioned first, second, third and fourth positions are arranged at apexes of a regular square, respectively. The wafers are transferred at the same time by a cross-shaped rotary arm (a cross arm) which has the rotational axis at the center of the regular square, and extends to the four apexes of the regular square. That is, a wafer chuck for gripping a wafer is provided at each end of the cross arm, and the cross arm is rotated by 90.degree. to simultaneously transfer the wafers from the first, second and third positions to the second, third and fourth positions, respectively.
Japanese Patent Provisional Publication No. 63-288642 has disclosed a V-shaped rotary arm (a V-shaped arm) which is an improvement of the cross arm disclosed by the Japanese Patent Provisional Publication No. 60-214911. The V-shaped arm is composed of rotary arms which are extended to two adjacent apexes of a regular square. According to the V-shaped arm, there are two wafer chucks of the rotary arm. If there is the wafer chuck at one of the position where maintenance is performed, the wafer chuck can easily retreat by rotating the rotary arm so that a maintenance space can be secured. The V-shaped arm rotates by a predetermined angle to simultaneously transfer the wafers from the first and second positions to the second and third positions, respectively. The wafer which has been cleansed at the third position is transferred at an appropriate time during the cutting of a following wafer. Thus, the wafer does not have to wait at the wafer cutting part where the wafer is transferred from and to the second position. For this reason, the transfer efficiency is substantially the same as that of the cross arm, and one wafer can be machined within the same period of time.
Each of the above-described cross arm and V-shaped arm transfers the wafers to describe a circular arc around the rotational axis, which is located at the center of the first, second, third and fourth positions. For this reason, a broad space is required compared to the case when the wafer is moved straight to the next position. Since the rotational axis is provided at the center of the first, second, third and fourth positions, the maintenance is difficult and the space cannot be saved.
Moreover, since sludge adheres to the wafer which has been cut by the wafer cutting part and has been unloaded at the second position, the sludge also adheres to the wafer chuck of the rotary arm which transfers the wafer from the second position to the third position. For this reason, the rotary arm to which the sludge adheres is used only for transferring the wafer from the second position to the third position, thereby preventing the spread of the sludge. The rotary arm to which the sludge adheres, however, passes over the first, second, third and fourth positions during rotation, and may strew the sludge over these positions.